Metal Gear Acid Cheats

Jehuty card:
     Enter "JEHUTY" as a password

Karen card:
     Enter "KAREN" as a password

Mika card:
     Enter "MIKA" as a password

Viper card:
     Enter "VIPER" as a password

XM8 card:
     Enter "XMEIGHT" as a password

Type xmeight and you will get the xm8 gun.

Successfully complete Stage 06 to unlock the "Link Battle" selection at the "Options" menu under the "Intermission" screen.

All of these are the passwords and names of the cards.

JEHUTY
KAREN
MIKA
VIPER
For xm8 type in XMEIGHT
Hopes this helps.